Objective. To investigate whether the synthesis of cartilage matrix protein (CMP) is enhanced in arthritic cartilage. Methods. The content of CMP in human and pig cartilage was determined by immunoblotting, and CMP- producing chondrocytes in osteoarthritic (OA) and rheumatoid arthritic (RA) joints were immunostained. Results. CMP was undetectable in the condylar cartilage and disc of pigs, whereas it was abundant in the rib and tracheal cartilage of the same animals. By immunohistochemical analysis, CMP was localized in only a few chondrocytes (5%) in normal human joints, whereas numerous chondrocytes (> 60%) were immunostained in RA joints. The number of CMP-producing cells was also increased in OA cartilage (>40%). Immunoblotting analyses confirmed that the CMP content in the cartilage from OA and RA patients was much higher than that in normal cartilage. Conclusion. These findings demonstrate that articular chondrocytes can synthesize CMP, although it is suppressed under physiologic conditions. The results also suggest that articular chondrocytes express CMP in response to arthritic stimuli.
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